1. Field of the Invention
The present invention relates to a photodetector integratable light coupling apparatus and, more specifically, to a light coupling apparatus that forms an etch-structure complex comprising a total reflection surface/an anti-reflection surface within a substrate to improve coupling efficiency with an incident light and responsivity of a photodetector device.
2. Discussion of Related Art
Recently, there has been a need that a photodetector should have an ultra-high-speed operating characteristic from several tens of GHz to several hundreds of GHz and high responsivity characteristic due to a rapid increase in a quantity of data transmitted over wired/wireless communication, and a request for high definition of an image processing system.
Moreover, a small and thin light absorption layer has been used in the photodetector to accomplish the high-speed operating characteristics, which leads to reducing the efficiency/responsivity of the photodetector. Therefore, technology development is urgently needed that effectively connects the incident light from outside to the photodetector and increases the responsivity of the photodetector operating at the high speed.
For improving the coupling efficiency between an external light transmission apparatus and the photodetector, so far, a method of integrating a coupling apparatus, such as a refracting-facet photodetector, a waveguide photodetector, and a spot-size converter, and a method of making an optical path longer in the light absorption layer using the total reflection surface have been known. In addition, there is a resonant-cavity photodetector that forms a high reflection mirror above and below an active layer including the light absorption layer to enhance the light coupling efficiency and responsivity, which have a disadvantage that results in complexity and difficulty of an epi structure for stacking the mirror, an increase in costs, and limiting wavelength selectivity to a narrow bandwidth.
Meanwhile, exemplary embodiments of the prior arts in connection with the improvement of the light coupling efficiency using a sloping facet are disclosed in U.S. Pat. No. 4,893,162 to Gentner, etc. and U.S. Pat. No. 6,049,638 issued 2000 to Norimatsu, etc.
U.S. Pat. No. 4,893,162 to Gentner, etc. is directed to a waveguide structure that forms one or two non-absorptive waveguide, III–V compound semiconductor, to attempt an evanescent coupling or a coupling with the photodetector by reflection at an etch surface. The etch surface used herein is formed at the end of the waveguide so that light along the waveguide can be reflected to enter into the photodetector portion.
U.S. Pat. No. 6,049,638 to Norimatsu, etc. is directed to the improvement of the light coupling efficiency using a refraction at an interface, and relates to a structure that the incident light refracted at one etch surface is reflected on another etch surface to enter into the photodetector.
There is still a room for improvement in a method of coupling the waveguide and external light for the above invention to Gentner, etc., and a method of coupling the etch surface to be an incident surface with refraction facet and external light for the above invention to Norimatsu, etc. Further, for the above inventions, a problem exists that a light coupling between the external light and the photodetector just depends on edge-coupled or bottom-side illumination, thus limiting an arranging method that can be selected upon packaging.